FIG. 11 shows a conventional synchronous motor equipped with interior magnets and a stator using concentrated windings. As shown in FIG. 11, the motor includes a stator 1 having concentrated windings, a rotor 2, slits 3 provided in the rotor, permanent magnets 4 located in the slits 3. Stator 1 is formed of a concentrated-winding stator having three phases, four poles and six slots. As shown in FIG. 12, respective teeth are wound with windings independently, and each phase includes two coils 180 degrees apart from each other, i.e., opposite to each other. Slits 3 shaped like a flat plate are prepared inside rotor 2, and permanent magnets having a similar shape to slit 3 are inserted in slits 3 respectively. As shown in FIG. 12, a motor using the concentrated windings provides independent windings to respective teeth, so that its coil ends are smaller than those of a distributed-winding stator, where the windings straddle over plural teeth. Thus wire-wound resistance becomes less, and copper loss caused by heat of the windings due to current running through the motor can be reduced. As a result, a highly efficient motor with smaller loss is obtainable.
The concentrated windings as shown in FIG. 11 have teeth wound with coils respectively, and the coils of respective phases are adjacent to each other. This structure produces greater inductance. The combination of this stator with a rotor having interior magnets produces magnetic salient poles in the rotor, so that reluctance torque becomes available. However, this structure increases inductance, and a lot of magnetic flux flows into the flux path along axis “q”, and the flux path pulls the magnetic flux into the rotor as shown in FIG. 11. Thus a magnetic flux density of the core substantially increases. As a result, iron loss greatly increases although the copper loss decreases, so that efficiency is lowered, which render the advantage of the concentrated windings insignificant. The present invention addresses the foregoing problem, and aims to provide a rotor of a synchronous motor having the concentrated windings. This rotor advantageously lowers the magnetic flux density of the stator core, and yet reduces copper loss and iron loss.